An Analysis of Human Kidney Cell Oxygen-Enhancement Ratios for Fast-Neutron Beams and a Prediction for Negative Pion Beams

Abstract

A semiphenomenological theory is developed to estimate survival curves of human kidney (T-1) cells in vitro from irradiation by particle beams that produce broad LET distributions. "Track segment" data are used in the low LET range by a straightforward generalization. The heavy recoils (Z > 2) from nuclear interactions, however, are treated separately. The assumption is made that such recoils inside the cell nucleus inactivate and those outside do not. Calculated oxygen-enhancement ratios from 3- and 15-MeV monoenergetic neutron beams compare favorably with experimental results; thus the constancy of this ratio as a function of neutron energy is quantitatively understood. The survival curves, however, agree less well with experiment, perhaps due to inadequate assumptions made for the inactivation cross sections of low energy protons, for which no experimental data are available. The oxygen-enhancement ratio in the peak dose region of a stopping π- beam is calculated to be between 1.8 and 2.0, slightly hig...